Harmonisation of stratospheric NO 2 /O 3 column data products NORS/NDACC UV-VIS meeting, Brussels, 3-4 July F. Hendrick and M. Van Roozendael Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium + NDACC UV-VIS Working Group

Context NDACC UV-vis Working Group meeting at British Antarctic Survey in November 2007: « There is a need to harmonize stratospheric O 3 and NO 2 column retrievals » Main reasons: Lack of consistency between the stations due to the use of different DOAS settings (e.g., NO 2 XS at different temperature) and AMFs Satellite groups encountered problems in the validation of their data using the NDACC UV-vis database, e.g. Wetzel et al., ACP, 2007 for the validation of MIPAS NO 2 NORS/NDACC UV-VIS meeting, Brussels, 3-4 July

Harmonisation of O 3 column retrieval: 1. DOAS settings NORS/NDACC UV-VIS meeting, Brussels, 3-4 July ParameterRecommendation Fitting interval nm Wavelength calibrationsolar atlas Cross sections O3O3 Bogumil et al. (2003), 223°K NO 2 Vandaele et al. (1998), 220°K H2OH2OHitran 2004 (Rothman et al., 2005) O4O4 Hermans ( Ring effectNDACC source for Ring effect correction Molecular and aerosol scattering Polynomial of order 3, or equivalent non- polynomial high-pass filtering AMF calculationBIRA-IASB O 3 AMF LUTs Determination of residual amount in reference spectrum Langley plot (Vaughan et al., 1997) SZA range for twilight averaging of vertical columns 86-91°SZA

Harmonisation of O 3 column retrieval: 2. O 3 AMF look-up tables NORS/NDACC UV-VIS meeting, Brussels, 3-4 July TOMS V8 (TV8) ozone and temperature profile climatology (Bhartia, 2004; McPeters et al., 2007) + total O 3 column dependence ParameterValue O 3 profileTV8: - Latitude: 85°S to 85°N step 10° - Month: 1 (Jan) to 12 (Dec) step 1 - Ozone column: 125 to 575 DU step 50 DU Temperature and pressure profiles TV8 Altitude grid0 to 120 km step 1 km Wavelength440 to 580 nm step 35 nm Surface albedo0 and 1 Altitude0 and 4 km SZA30, 50, 70, 80, 82.5, 85, 86, 87, 88, 89, 90, 91, and 92° LUTs, AMF extraction routine as well as DOAS settings publicly available at:

Validation of new retrieval settings NORS/NDACC UV-VIS meeting, Brussels, 3-4 July V1V2Corr temp Comparison to: Dobson at OHP (44°N, 5.5°E) Amplitude of Dobson-SAOZ seasonal variation: V1 6.9% SAOZ Yearly AMF V2 3.2% SAOZ LUT AMF Bias / Std Dev after temperature correction: -1.2% ± 3.7% Brewer at Sodankyla (67°N, 27°E) Amplitude of Brewer-SAOZ seasonal variation: V1 6.5% SAOZ Yearly AMF V2 2.4% SAOZ LUT AMF Bias / Std Dev after temperature correction: 1.9% ± 3.2%

Impact on the difference satellites - SAOZ NORS/NDACC UV-VIS meeting, Brussels, 3-4 July Reduced amplitude of seasonal variation Reduced bias V1 Yearly AMF V2 LUT AMF More details on the recommendation and comparison studies in Hendrick et al., ACP, 2011

Harmonisation of NO 2 column retrieval: 1. DOAS settings NORS/NDACC UV-VIS meeting, Brussels, 3-4 July ParameterRecommendation Fitting interval nm Wavelength calibrationsolar atlas Cross sections NO 2 Vandaele et al. (1998), 220°K O3O3 Bogumil et al. (2003), 223°K H2OH2OHitran 2004 (Rothman et al., 2005) O4O4 Hermans ( Ring effectChance and Spurr (1997) Molecular and aerosol scattering Off-set correction Polynomial of order 3 to 5 maximum, or equivalent non-polynomial high-pass filtering Slope AMF calculationBIRA-IASB NO 2 AMF LUTs Determination of residual amount in reference spectrum Modified Langley plot (Vaughan et al., 1997) SZA range for twilight averaging of vertical columns 86-91°SZA

Harmonisation of NO 2 column retrieval: 2. Stratospheric NO 2 AMF LUTs NORS/NDACC UV-VIS meeting, Brussels, 3-4 July LUTs, AMF extraction routine as well as DOAS settings publicly available at: ParameterValues Lambert et al.’s NO 2 profile climatology - Latitude: 85°S to 85°N step 10° - Month: 1 (Jan) to 12 (Dec) step 1 - Sunrise and sunset - Altitude range : km SAOZ balloon NO 2 profile climatology - Latitude: tropics, mid- and high-latitudes - Resolved in seasons (spring, summer, fall, winter) - Altitude range: km Wavelength350 to 550 nm step 40 nm Surface albedo0 and 1 Altitude of the station 0 and 4 km SZA10, 30, 50, 70, 80, 82.5, 85, 86, 87, 88, 89, 90, 91, and 92° Lambert et al.’s climatology consists of a Fourier harmonic decomposition of UARS HALOE v19 and SPOT-4 POAM-III v2 NO 2 profile data records.

NO 2 questionnaire (1) NORS/NDACC UV-VIS meeting, Brussels, 3-4 July

NO 2 questionnaire (2) NORS/NDACC UV-VIS meeting, Brussels, 3-4 July QuestionRecommendation Correction for the variation of the stratospheric t° (around 220K) ? Temperature correction using a simple monthly zonal climatology of temperature profiles. Could be coupled to the AMF climatology. Filtering of the data conta- minated by tropospheric NO 2 Langley-plot method (data points not lying on 'smooth‘ lines indicate a tropospheric contamination) Explicit correction for the impact of the Ring effect on the NO 2 SCDs ? post-processing option, based on simple SZA parameterization Should we take into account the NO 2 photochemistry and its impact on the AMF ? Sensitivity tests needed. Explicit correction is rather complex to implement. Could be included in the error budget Best estimates of the random and systematic uncertainties ? Random uncertainty derived from fitting residuals. Systematic uncertainty to be estimated off-line based on sensitivity studies. Should be performed for each station. Note that both errors must be provided separately according to GEOMS. AMF correction for the period affected by the Pinatubo aerosols ? Sensitivity tests needed. Not easy to include in standard recommendations.

Impact of aerosols NORS/NDACC UV-VIS meeting, Brussels, 3-4 July % -10% 0 -5% -10%

Satellites (TEMIS) - SAOZ NORS/NDACC UV-VIS meeting, Brussels, 3-4 July GOME-2 - SAOZSCIAMACHY-SAOZ GOME-SAOZOMI-SAOZ